Jet engine aircraft achieve forward thrust by ejecting gas rearwardly during flight. Reverse thrust is used to decelerate the aircraft. This is achieved by throttling or closing the rear exhaust and directing gas radially from the aircraft with some forward component.
When used in flight, pitch and yaw control is desirable in combination with this reverse thrust. This may be achieved with reverser doors located in the reverser duct. Relative opening of the top and lower door sets will produce pitch control. Splaying the doors transverse to the aircraft center line will produce yaw.
The amount of opening of the doors and the splay of the doors must be modulated. The control system is simplified if the linkage can be arranged where control of one actuator would control the opening of the doors and control of a second actuator would control the splay of the doors.